I do not know much about the aberrations of the TM2 solo system since I don't have TM2 myself. However, I think most of it is the same as it TM1.
As I mentioned above it is less likely to equal someone in TM2. First of all, the number of players is usually increasing day after day. The points of the top players and your own points do probably not update simultaneously. The value for the number of players per map may also differ from the real number of players because of equal records (records with a difference of not more than 0.001), which share their points (the points of the specific ranks are added and divided by the number of the same ranks). It is, as you said, only correct if you know that no one did your time.
So, I think this formula might better be applied to maps where it is generally unlikely to equal someone, like d or e maps. They are longer, the records scatter over a wider range, and they have generally less records, hence less equal times and more precise results.
